1. Field of the Invention
The present invention relates to a printing apparatus and processing method thereof.
2. Description of the Related Art
Recently, it has become possible to manufacture high-density, long printheads. Such a printhead is generally called a full-line head or the like, and can complete an image by one printing scan in a wide printing area.
The full-line head has a larger number of nozzles than a conventional serial scan head. It is difficult to maintain the discharge state of all nozzles normally, and a discharge failure nozzle is highly likely to be generated. Causes of generating a discharge failure nozzle include various factors such as paper dust or mote attaching near a nozzle, attachment of an ink mist, an increase in ink viscosity, and mixing of bubbles or dust into ink.
Sudden generation of a discharge failure nozzle during the printing operation leads to degradation in image quality. This boosts the demand for a technique to allow quick detection of a discharge failure nozzle and maintain image quality. As a method for detecting a discharge failure nozzle, a technique disclosed in Japanese Patent Laid-Open No. 2011-101964 has been known.
In Japanese Patent Laid-Open No. 2011-101964, a line type inkjet head prints by a plurality of lines for each color, and a line sensor acquires each density data. Accumulated density data is acquired by accumulating density data for a plurality of lines for each color. The accumulated density data is compared with a threshold to specify a discharge failure nozzle.
The line sensor used in Japanese Patent Laid-Open No. 2011-101964 is formed by arraying a plurality of CCD elements in one line. If the detection sensitivities of these CCD elements are not constant, accurate density data cannot be measured, and a discharge failure nozzle will fail to be specified. In this case, neither printhead recovery processing nor image supplement using another nozzle can be performed, degrading the image quality.
The present invention has been made to solve the above problems, and has as its object to provide a high-reliability inkjet printing apparatus capable of accurately specifying a discharge failure nozzle and maintaining the image quality even if the detection sensitivity of a line sensor configured to detect an inspection pattern is not constant.